Recently, it is seen that planarization of surfaces of interconnect substrates for large scale semiconductor integrated circuits (referred to as “LSI”s hereafter) is important. One of representative techniques for the planalization is the Chemical Mechanical Polishing; CMP (referred to as “polishing” as long as there is not any notification).
The polishing techniques are classified roughly into two processes:
a process utilizing a mechanical polishing property of abrasive grains; and
a process dominantly utilizing a chemical surface reaction effect with polishing with abrasive grains enhancing the reaction.
The former process is mainly used for planarization of insulator films such as silicon oxide (SiO2), alumina (Al2O3), or silicon nitride (SiN). An example, in which polishing of SiO2 is applied to semiconductor integrated circuit fabrication, is described, for example, “PROCEEDINGS VLSI MULTILEVEL INTERCONNECT CONFERRENCE 1991, A POUR-LEVEL-METAL FULLY PLANARIZED INTERCONNECT TECHNOLOGY FOR DENSE HIGH PERFORMANCE LOGIC AND SRAM APPLICATIONS” 20-26. Concentration of abrasive grain in slurries for these polishing process is generally high, often ranging in 10-25 weight percent.
The latter process, in which chemical reaction mainly works, is mainly used for metal-film planarization, and described in detail, for example, in JP-A-2-278822 specification and JP-A-8-83780. Concentration of abrasive grain in the slurries is often 5 weight percent or less. A process, in which metal-films are polished in a liquid containing substantially no abrasive grain, is disclosed JP-A-11-195628.
It is assumed that an in-between process of the above two processes is polishing of (Si) substrate. Slurry for insulator is used in the substrate polishing, but it is thought that dominance of chemical reaction effect with respect to mechanical polishing effect in the substrate polishing process is greater than the one in SiO2 polishing process.
Additionally, processes to polish silicon wafers, glass substrates, or the like, in which instead of polymer-resin polishing pad, a polishing pad with fixed abrasive grains such as silica or cerium oxide (referred to as “grindstone” hereafter) is used and slurry itself does not contain any abrasive grain, are disclosed in such as JP-A-10-125880 or JP-A-8-64562. A process to polish copper using similar grindstone is described in “PROCEEDINGS SEMI TECHNOLOGY SYMPOSIUM 1998, A NEW SLURRY-FREE CMP TECHNIQUE FOR CU INTERCONNECTS” 5-72 to 5-78. However consideration must be made, since principle of each of above methods using such fixed abrasive grains is similar to principle of polishing using slurry with respective abrasive grain and therefor the method easily generate polishing damage while having good planarizing effect.
It is necessary that polishing is performed uniformly over a predetermined area of an interconnect Wafer when above mentioned polishing process is applied for planarization of surface of the interconnect wafer. In order that polishing is performed uniformly, it is needed that at least a surface of an interconnect wafer, which is to be polished, is pressed onto a polishing pad with uniform pressure. For uniform pressing, a variety of polishing apparatuses, particularly carrier structures to hold an interconnect substrate therein and mechanism for applying uniform pressure onto an interconnect substrate in the carriers, are being developed.
Fluid pressing mechanism is known as a carrier structure suitable for uniform pressing. As the fluid pressing mechanism, two type is known; a type of mechanism in which pressure is applied with air or liquid onto backside of an interconnect wafer (referred to as “direct fluid pressing mechanism” hereafter), and a type of mechanism in which pressure is applied by pressing a flexible rubber-like sealed bag onto backside of an interconnect substrate (referred to as “fluid bag mechanism”).
The latter, as an example described in “The Japan Society for Precision Engineering, Autumn Conference 1991, conference paper publication, TRIAL MANUFACTURE AND BASIC CHARACTERISTICS OF POLISHING APAPRATUS” 211-212, has a structure wherein pressure applied onto a carrier is transmitted through a fluid bag constituted by a balloon-like membrane to an interconnect substrate and wherein an annular retainer surrounds an interconnect substrate to confine the substrate during polishing. Pressing onto an interconnect substrate is carried out by filling gas within the fluid bag. It is assumed that pressing with such fluid bag provides uniform pressing over backside of an interconnect substrate. In this example, the fluid bag is not secured to periphery of a substrate. Sealed container filled with fluid is pressurized by a weight. Since the weight or the fluid bag is not fixed, a guide is further provided outside of the retainer in order to prevent them coming off.
As described above, polishing apparatuses in which a weight or a fluid bag is not secured to a guide, are not suitable for polishing of many interconnect substrates since load and unload of an interconnect substrate are complicated. To solve the problem, a mechanism wherein a fluid bag is secured to a carrier is used recently.
The portion of a carrier that contacts with an interconnect substrate is provided with substantially planar surface, since once foreign materials infiltrate into the mechanism when polishing is performed they may generate polishing damage or contamination. For example, surface and inner surface of the retainer are finished with surface smoothness such that they have luster. A membrane composing the fluid bag is flexible and made of flexible rubber material with large friction such as neoprene or soft silicone. Therefor the membrane does not have luster like the retainer, but is finished with generally smooth surface. In the direct fluid pressing mechanism, rubber-like or polymer-resin-like layer with smooth surface is made contact only with periphery of backside of an interconnect substrate, and pressing is then carried out by increasing fluid pressure on the backside of the interconnect substrate while retaining them in sealed states or the similar states.
In all cases above mentioned for fluid pressing mechanism, torque for rotating an interconnect substrate is first applied to the carrier, then applied to the interconnect substrate through elastic material or thin film of rubber-like material or polymer resin. The interconnect substrate is thus supported flexibly, and a characteristic is provided that a substrate is secured to carrier or other transfer mechanism while allowing twist and eccentricity. Such mechanism in a polishing apparatus with fluid pressing mechanism consists of membrane composing flexible portion contacting with an interconnect substrate and a flexor that connects a carrier with the membrane.
As described above, for use in polishing of interconnect substrates for such as semiconductor integrated circuit devices, a variety of slurries that have not only mechanical effect but also surface chemical reaction effect, and polishing apparatuses comprising a carrier with fluid pressing mechanism such as fluid bags, have been developed.
However, a problem for unstable polishing arise in that polishing by using such polishing apparatus with fluid pressing mechanism and chemical-effect-dominant slurry often results in periodical high frequency sound (high frequency noise) generation and significantly lowered polishing rate. Such unstable polishing usually does not occur when slurry for insulator is used, but frequently occurs when slurry utilizing surface chemical reaction and having abrasive grain at concentration of 5 weight percent or less, i.e. slurry for metal containing substantially no abrasive grain, is used. When slurry substantially no abrasive grain is used, unstable polishing does not occur if a conventional polishing apparatus with pressing mechanism other than fluid pressing mechanism.
As described above, there is a problem that it is difficult to utilize in stable manner the combination of chemical-reaction-dominant slurry containing low or substantially no abrasive grain and causing little surface damage of interconnect substrates, and a polishing apparatus with fluid pressing mechanism providing good uniformity.